As a driving method of a light emitting device that is one of display devices, there is known a time gray scale method in which a light emission period of a pixel in one frame period is controlled with a binary voltage of a digital video signal to display a gray scale. Electroluminescent materials are more suitable for a time gray scale method than liquid crystals and the like since the response rate is generally faster. Specifically, when performing display by the time gray scale method, one frame period is divided into a plurality of subframe periods. Then, a pixel emits light or not in accordance with a video signal in each subframe period. According to the aforementioned structure, the total actual light emission period of the pixel in one frame period can be controlled by a video signal, so that a gray scale can be displayed.
However, in the case of performing display using the time gray scale method, there is a problem in that a pseudo contour is displayed in a pixel portion depending on the frame frequency. Pseudo contours are unnatural contour lines that are often perceived when the middle gray scale is displayed by the time gray scale method, which are considered to be mainly caused by a variation of the perceptual luminance due to the characteristic of human visual sense.
As a technique to prevent the above-described pseudo contour, a driving method of a plasma display has been proposed in which a subframe period for light emission appears continuously within one frame period in the following Patent Document 1. According to the driving method, such a phenomenon that a light emission period and a non-light emission period within each frame period are inverted in adjacent frame periods can be prevented, so that generation of a pseudo contour can be suppressed.
[Patent Document 1] Japanese Patent Laid-Open No. 2000-231362